Hydrothermal systems involving dormant faults within orogenic belts are rarely targeted for geothermal exploration, partly because of the complexity of the 3‐D topography, the unknown permeability of the fault zones and the basement lithology, and the lack of deep‐level data. This study brings together various types of surface information (spring features, geological data, topography, and hydrochemistry) to explain the alignment of 29 hot springs (29–73 °C) along the dormant Têt fault (Eastern Pyrénées, France). Water ion concentrations, stable water isotopes, and lithium isotopic ratios indicate that (i) fluids originating from meteoric water infiltrate above an altitude of 2,000 m, (ii) the rocks interacting with the fluids are similar for all the springs, and (iii) the maximum fluid temperatures at depth show similar variations along the fault and at the surface. A 3‐D numerical model of the system, assembled from field structural data and from a digital elevation model, explores the permeability combinations for the basement and for a three‐fault network. The models indicate that for a relatively permeable basement (10⁻¹⁶ m²), fluids are topography‐driven down to thousands of meters (until −3,700 m) before being captured by the more permeable Têt fault. Hot spring temperatures can be numerically reproduced when fault permeability is around 10⁻¹⁴ m², a value slightly lower than the critical permeability for which free convection would occur within the Têt fault. Our study shows that thermal anomalies are possible along dormant faults close to elevated topography in the core of an orogenic belt, thereby opening new perspectives for geothermal exploration.

The way faults control upward fluid flow in nonmagmatic hydrothermal systems in extensional context is still unclear. In the Eastern Pyrénées, an alignment of twenty-nine hot springs (29°C to 73°C), along the normal Têt fault, offers the opportunity to study this process. Using an integrated multiscale geological approach including mapping, remote sensing, and macro- and microscopic analyses of fault zones, we show that emergence is always located in crystalline rocks at gneiss-metasediments contacts, mostly in the Têt fault footwall. The hot springs distribution is related to high topographic reliefs, which are associated with fault throw and segmentation. In more detail, emergence localizes either (1) in brittle fault damage zones at the intersection between the Têt fault and subsidiary faults or (2) in ductile faults where dissolution cavities are observed along foliations, allowing juxtaposition of metasediments. Using these observations and 2D simple numerical simulation, we propose a hydrogeological model of upward hydrothermal flow. Meteoric fluids, infiltrated at high elevation in the fault footwall relief, get warmer at depth because of the geothermal gradient. Topography-related hydraulic gradient and buoyancy forces cause hot fluid rise along permeability anisotropies associated with lithological juxtapositions, fracture, and fault zone compositions.

Rare metals are essential to the development of the “green” technologies that are at the core of low-carbon societies. In nature, these metals are frequently present in trace amounts scattered in base metal ore deposits, but the physico-chemical processes that are responsible for their concentration into strategic minerals are still poorly understood. Based on laser-induced breakdown spectroscopy (LIBS), coupled with electron backscattered diffraction (EBSD) analysis, this study shows that plastic deformation and subsequent syntectonic recrystallization of sphalerite (zinc sulfide, ZnS) led to the spatial redistribution of germanium (Ge): from a background level of a few hundreds of parts per million in undeformed primary sphalerite to tens of weight-percent in neocrystallized Ge minerals. During dynamic recrystallization, Ge is likely released from the crystal lattice of parent sphalerite and subsequently concentrated in Ge minerals, leaving behind a Ge-depleted, recrystallized sphalerite matrix. Identifying how rare metals concentrate through deformation and syntectonic recrystallization at the mineral scale is essential to understand the spatial redistribution and localization at the deposit scale. This study highlights the importance of coupling in situ chemical mapping analysis with macro- and microstructural characterization when targeting rare metals in deformed ore.